Calculate in join in sql - sql

Question

I am trying to achieve staggered calculation in joins in sql 2008. I can have n number of rows for 1 job id. I have created a sample below
CREATE TABLE Job
(
JobID INT NOT NULL,
Amount INT NOT NULL
);
INSERT INTO Job (JobID, Amount)
VALUES (1, 25),
(1, 45),
(1, 40),
(2, 25),
(3, 26),
(3, 26);
now the discount for JobID = 1 is 80 , So what I am expecting in output of query result is below:
If the Amount > Discount , so show the finalvalue = Amount - Discount
but if Amount < Discount , then show Finalvalue = Amount - Amount ,
and if Discount is still left , deduct the same from the subsequent rows.
Job ID Amount FinalValue
1 25 0
1 45 0
1 40 30
Can all this be done in a join?

Answer 1

Here you are:
EDIT: ATTENTION: You should add a column for sorting. My approach is partitioning AND sorting by JobID which makes the output random...
EDIT: Sorry, did not add the tables...
CREATE TABLE Job
(
JobID INT NOT NULL,
Amount INT NOT NULL
);
INSERT INTO Job (JobID, Amount)
VALUES (1, 25), (1, 45), (1, 40), (2, 25), (3, 26), (3, 26);
CREATE TABLE Discount
(
JobID INT NOT NULL,
Discount INT NOT NULL
);
INSERT INTO Discount(JobID,Discount)VALUES(1,80),(2,0),(3,10);
WITH myCTE AS
(
SELECT ROW_NUMBER() OVER(PARTITION BY Job.JobID ORDER BY Job.JobID) AS inx
,Job.JobID
,Job.Amount
,Discount.Discount
FROM Job
INNER JOIN Discount ON Job.JobID=Discount.JobID
)
SELECT * FROM myCTE
CROSS APPLY
(
SELECT SUM(x.Amount)
FROM myCTE AS x
WHERE x.JobID=myCTE.JobID
AND x.inx<=myCTE.inx
) AS AmountCummulativ(AmountCummulativ)
CROSS APPLY(SELECT AmountCummulativ-myCTE.Discount) AS DiscountCalculated(DiscountCalculated)
CROSS APPLY(SELECT CASE WHEN DiscountCalculated<0 THEN 0 ELSE DiscountCalculated END) AS DiscountResolved(DiscountResolved)
Hope this helps

Answer 2

I think what you are looking for can be done using a case statement
select a.jobid,a.Amount,case when a.amount > b.discount then a.amount - b.discount else 0 end final_value
from Job a inner join Job_discount b on a.jobid = b.jobid
You can look at the results here http://sqlfiddle.com/#!3/f9a46/1
I had to assume the discount table structure

Answer 3

I added some sequence (row number) for the Job table (calling it JobOrder), to increment the sums. You can change the order as it is now for JobId, Amount!
With JobOrder as (
-- Job order by id and amount
select row_number() over (order by JobID, Amount asc) as rowno, JobId, Amount from Job
),
JobSumIncr as (
select
JobID,
Amount,
(select sum(Amount)
from JobOrder j2
where j2.JobID = j.JobID and j2.RowNo <= j.RowNo
) as AmountTotal
from JobOrder j
)
select
j.JobID,
j.Amount,
j.AmountTotal,
d.Discount,
(case when d.Discount>=j.AmountTotal then 0 else j.AmountTotal-d.Discount end) as FinalValue
from
JobSumIncr j left join Discount d on j.JobID = d.JobID;
Asuming that your Discount table is something like:
CREATE TABLE Discount (
JobID INT,
Discount INT
);
SqlFiddle here! and for a more secure Sql (checking null values and see the discount left) see this SQLFiddle too.
A version which keeps track of the discount left, see sqlfiddle-2 above.

Answer 4

You can try following code : 80 is the discount amount
Select JobID, Amount,
case when SUM (Amount) OVER (partition by JobID ORDER BY JobID ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) > 80 then SUM(Amount) OVER (partition by JobID ORDER BY JobID ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) - 80 else 0 end as FinalValue
from Job